A core of a stator (referred to as a stator core as necessary in descriptions below) of a rotating electrical machine of a generator, an electric motor, or the like is formed by laminating metal plates such as a magnetic steel sheet. The stator core includes a yoke that extends in a circumferential direction of the stator core, and a plurality of teeth that extend in a direction of a rotating shaft from an inner circumferential surface of the yoke. In order to manufacture the stator core, a core piece, which has the same shape as the shape (shape on the plate surface) when viewed from thickness directions of the yoke and the teeth, is punched from a metal plate, and the core pieces are laminated in the thickness direction.
In the stator core manufactured as described above, at the time of the manufacturing, since elastic deformation does not occur in a surface direction, the magnetic characteristics are excellent. However, the outer circumferential shape of the yoke is circular, and except in the portions where the teeth are formed, the more inward portion than the inner circumference of the yoke is opened. Accordingly, if the stator core is manufactured in this way, many unused portions occur in the metal plate that is used for punching. Therefore, the yield of the metal plate is decreased, and the material costs are increased.
Thus, a helical core is used as the stator core in a rotating electrical machine such as a generator for a vehicle. The helical core is formed by laminating belt-shaped metal plates that are formed in shapes corresponding to the yoke and the teeth while processing the metal plates into a helical shape by bending in the plate surface. For example, the helical core is suitably used in a core for a rotating electrical machine in which the diameter is 50 mm or more and 300 mm or less. In this case, for example, as the metal plate for the helical core, a belt-shaped metal plate, in which the plate thickness is 0.15 mm or more and 0.80 mm or less, is suitably used. However, if the bending process in the plate surface is performed on the belt-shaped metal plate, the outer circumferential side of the portion corresponding to the yoke of the belt-shaped metal plate extends more largely than the inner circumferential side, and there is a concern that the thickness of the outer circumferential side of the belt-shaped metal plate (yoke) may be thinner than the thickness of the inner circumferential side.
Thereby, in Patent Document 1, magnetic powder is filled in a gap that is generated at the outer circumferential side of the core due to the fact that the outer circumferential side of the portion corresponding to the yoke of the belt-shaped metal plate more largely extends than the inner circumferential side. In this way, magnetic characteristics and stiffness of the core can be recovered.
Moreover, in Patent Document 2, a belt-shaped metal plate that is formed in a shape corresponding to the yoke and the teeth is divided into a plurality of core pieces. The circumference (the outer circumference of the portion corresponding to the yoke) of each core piece is formed in an arc shape conforming to the shape of the yoke. Moreover, the core pieces adjacent to each other are connected to each other by a connection portion that is formed on the outer circumferential side of the side end of the core piece, and each of core pieces, which is connected to each other by the connection portion, linearly extends. If the plurality of core pieces are processed into a helical shape by the bending processing in the plate surface, the regions of the inner circumferential side rather than the connection portion in the side surfaces of the portions corresponding to the yokes of the core pieces adjacent to each other are joined, and the connection portion is deformed so as to be bent. Thereby, it is possible to prevent the outer circumferential side corresponding to the yoke of the belt-shaped metal plate from being thinner than the inner circumferential side.
Moreover, in Patent Document 3, a long belt-shaped silicon steel sheet is punched, teeth and notches are formed at a time so as to leave bridge portions, and a unit core element sheet is manufactured. Furthermore, after a laminated core is formed from the unit iron core element sheets, an insulating layer is formed on the laminated core. The material loss of the unit core element sheet is decreased by forming the notch on the unit core element sheet, and strength of the laminated core according to the formation of the notch is improved by forming the insulating layer on the laminated core.